This invention relates generally to plasma arc torches, and more particularly to a contact start plasma arc torch.
Plasma arc torches, also known as electric arc torches, are commonly used for cutting, welding, and spray bonding metal workpieces. Such torches typically operate by directing a plasma consisting of ionized gas particles toward the workpiece. In general, a pressurized gas to be ionized is directed through the torch to flow past an electrode before exiting the torch through an orifice in the torch tip. The electrode has a relatively negative potential and operates as a cathode. The torch tip, which is adjacent to the end of the electrode at the front end of the torch, constitutes a relatively positive potential anode. When a sufficiently high voltage is applied to the torch, an arc is established across the gap between the electrode and the torch tip, thereby heating the gas and causing it to ionize. The ionized gas in the gap is blown out of the torch and appears as a flame extending externally from the tip. As the torch head or front end is positioned close to the workpiece, the arc transfers between the electrode and the workpiece because the impedance of the workpiece to negative potential is typically lower than the impedance of the torch tip to negative potential. During this xe2x80x9ctransferred arcxe2x80x9d operation, the workpiece serves as the anode.
Plasma arc torches may be found in both xe2x80x9cnon-contact startxe2x80x9d and xe2x80x9ccontact startxe2x80x9d varieties. In non-contact start torches, the tip and electrode are normally maintained at a fixed physical separation in the torch head. Typically, a high voltage high frequency signal is applied to the electrode (relative to the tip) to establish a pilot arc between the electrode and the tip. As mentioned above, when the torch head is moved toward the workpiece, the arc transfers to the workpiece. By way of contrast, in conventional contact start torches, the tip and/or the electrode make electrical contact with each other generally at the bottom of the electrode. For example, a spring or other mechanical means biases the tip and/or electrode longitudinally such that the tip and electrode are biased into electrical contact to provide an electrically conductive path between the positive and negative sides of the power supply. When the operator squeezes the torch trigger, a voltage is applied to the electrode and pressurized gas flows through the torch to the exit orifice of the torch tip. The gas causes the tip and/or the electrode to overcome the bias and physically separate. As the tip and electrode separate, a pilot arc established therebetween is blown by the gas toward the exit orifice of the tip.
One disadvantage associated with the conventional contact start plasma torch described above is that repeated axial movement of the electrode, the tip or both can result in axial misalignment between the electrode and tip. Also, by establishing the pilot arc between the electrode and the tip at the bottom of the electrode, damage is caused to the tip adjacent the central exit orifice of the tip. Axial misalignment of the electrode and tip, as well as any damage to the tip, can result in decreased torch performance and/or cut quality. Consequently, frequent replacement of the tip is required. For conventional contact start torches in which the tip is movable for establishing electrical contact with the electrode, the tip is in different longitudinal positions in the on and off modes of the torch, making it cumbersome for an operator to control the relative position of the tip with respect to a workpiece being cut. It is also difficult to conduct drag cutting of a workpiece, where the tip is set down onto the workpiece during cutting, because the tip would be undesirably moved into contact with the electrode upon being set down onto the workpiece.
Among the several objects and features of the present invention is the provision of a contact start plasma torch and method of operating such a torch which reduces the frequency of torch tip replacement; the provision of such a torch and method which reduces the risk of axial misalignment between the electrode and the tip; the provision of such a torch which reduces the risk of tip damage adjacent the central exit orifice of the tip; and the provision of such a torch and method which eliminates the need for axial movement of the electrode and/or the tip to generate a pilot arc.
In general, a contact start plasma torch of the present invention comprises a cathode body adapted for electrical communication with the negative side of a power supply and an anode body adapted for electrical communication with the positive side of the power supply. A primary gas flow path directs working gas from a source of working gas through the torch. A conductive element of the torch is constructed of an electrically conductive material and is free from fixed connection with the cathode body and the anode body. The torch is operable between an idle mode in which the conductive element provides an electrically conductive path between the cathode body and the anode body and a pilot mode in which a pilot arc formed between the conductive element and at least one of said cathode body and said anode body is adapted for initiating operation of the torch by exhausting working gas in the primary gas flow path from the torch in the form of an ionized plasma.
Another embodiment of the present invention is directed to a contact start plasma torch of the type having a primary gas flow path for directing a working gas through the torch whereby the working gas is exhausted from the torch in the form of an ionized plasma. The torch of this embodiment generally comprises an electrode having a longitudinally extending side surface and a bottom surface. A tip surrounds the electrode in spaced relationship therewith to at least partially define the primary gas flow path of the torch for directing a working gas through the torch in a downstream direction. The tip has a central exit orifice in fluid communication with the primary gas flow path for exhausting working gas from the torch. The bottom surface of the electrode is in longitudinally opposed relationship with the central exit orifice of the tip. Opposed contact surfaces are disposed in the torch, with at least one of the contact surfaces being movable relative to the other one of the contact surfaces. The torch is operable between an idle mode in which the contact surfaces are positioned relative to each other to provide an electrically conductive path therebetween and a pilot mode in which the contact surfaces are in spaced relationship with each other whereby a pilot arc is formed between the contact surfaces. The contact surfaces are disposed in the torch upstream from the bottom surface of the electrode whereby the pilot arc is formed generally within the primary gas flow path upstream from the bottom surface of the electrode and is blown by working gas in the primary gas flow path toward the central exit orifice of the tip for exhausting working gas from the tip in the form of an ionized plasma.
A conductive element of the present invention is adapted for use in a contact start plasma torch of the type having an electrode in electrical communication with the negative side of a power supply and a tip surrounding the electrode in spaced relationship therewith to at least partially define a primary gas flow path of the torch, the tip being in electrical communication with the positive side of the power supply and having a central exit orifice in fluid communication with the primary gas flow path for exhausting working gas from the tip in the form of an ionized plasma. The conductive element generally comprises a generally cup-shaped body constructed of an electrically conductive material. The conductive element is adapted for movement relative to the electrode and the tip between a first position is corresponding to an idle mode of the torch in which the conductive element provides an electrically conductive path between the positive side of the power supply and the negative side of the power supply and a second position spaced from the first position of the conductive element. The second position of the conductive element corresponds to a pilot mode of the torch whereby movement of the conductive element toward its second position forms a pilot arc generally within the primary gas flow path capable of initiating operation of the torch for exhausting working gas from the torch in the form of an ionized plasma.
An electrode of the present invention is adapted for use in a contact start plasma torch of the type having a primary gas flow path for directing a working gas in a downstream direction through the torch, a tip surrounding the electrode in spaced relationship therewith to at least partially define the primary gas flow path of the torch, a contact surface in the torch for forming a pilot arc in primary gas flow path of the torch and a central exit orifice in the tip communicating with the primary gas flow path for exhausting working gas from the tip in the form of an ionized plasma. The electrode generally comprises a generally cylindrical body having a longitudinally extending side surface. A bottom surface of the electrode is oriented generally radially relative to the longitudinally extending side surface for longitudinally opposed positioning relative to the central exit orifice of the tip. A contact surface is disposed above the bottom surface of the electrode and is engageable with the contact surface said tip being generally cup-shaped and having a central exit opening adapted for fluid communication with the primary gas flow path for exhausting working gas from the tip in the form of an ionized plasma, the tip further having a top surface and an annular projection extending up from the top surface for use in radially positioning the tip in the torch.
A tip of the present invention is adapted for use in a contact start plasma torch of the type having a primary gas flow path for directing a working gas through the torch whereby the working gas is exhausted from the torch in the form of an ionized plasma. The tip is generally cup-shaped and has a central exit opening adapted for fluid communication with the primary gas flow path for exhausting working gas from the tip in the form of an ionized plasma. The tip further has a top surface and an annular projection extending up from the top surface for use in radially positioning the tip in the torch.
In another embodiment, a tip of the present invention is adapted for use in a plasma torch of the type having a primary gas flow path for directing a working gas through the torch whereby the working gas is exhausted from the torch in the form of an ionized plasma and a secondary gas flow path for directing gas through the torch whereby the gas is exhausted from the torch other than in the form of an ionized plasma. The tip is generally cup-shaped and has a central exit opening adapted for fluid communication with the primary gas flow path for exhausting working gas from the tip in the form of an ionized plasma. The tip further has at least one metering orifice adapted for fluid communication with the secondary gas flow path for metering the flow of gas through the secondary gas flow path.
A contact assembly of the present invention is adapted for use in a contact start plasma torch of the type having a primary gas flow path for directing a working gas through the torch, an electrode in electrical communication the negative side of a power supply and a tip surrounding the electrode in spaced relationship therewith to at least partially define the primary gas flow path of the torch. The contact assembly generally comprises a conductive element constructed of an electrically conductive material and an enclosure surrounding the conductive element in fluid communication with a source of pressurized gas for receiving gas into the enclosure. The conductive element is disposed at least partially within the enclosure and is moveable relative to the enclosure, the electrode and the tip in response to pressurized gas received in the enclosure whereby movement of the conductive element forms a pilot arc in the torch.
An electrode assembly of the present invention is adapted for use in a contact start plasma torch of the type having a cathode body adapted for electrical communication with the negative side of a power supply and an anode body adapted for electrical communication with the positive side of the power supply. The electrode assembly generally comprises an electrode extending longitudinally within the torch and defining at least in part the cathode body of the torch. An insulating sleeve surrounds at least a portion of the electrode and is constructed of an electrically non-conductive material to insulate the at least a portion of the electrode against electrical communication with the anode body of the torch.
A method of the present invention is used for starting a contact start plasma torch of the type having a cathode body in electrical communication with the negative side of a power supply and an anode body in electrical communication with the positive side of the power supply, with the anode body being positioned relative to the cathode body to at least partially define a primary gas flow path of the torch and the torch having a central exit orifice in fluid communication with the primary gas flow path for exhausting working gas from the torch in the form of an ionized plasma. The method generally comprises the act of causing an electrical current to flow along an electrically conductive path comprising the anode body, the cathode body and a conductive element electrically bridging the cathode body and the anode body in a first position of the conductive element corresponding to an idle mode of the torch. Working gas is directed from a source of working gas through the primary gas flow path of the torch. Movement of the conductive element relative to the cathode body and the anode body toward a second position corresponding to a pilot mode of the torch is effected whereby a pilot arc is formed between the conductive element and at least one of said cathode body and said anode body as the conductive element is moved toward its second position. The pilot arc is then blown through the primary gas flow path toward the central exit orifice of the torch such that working gas is exhausted from the primary gas flow path of the torch in the form of an ionized plasma.
In another embodiment, a method of the present invention involves starting a contact start plasma torch of the type having an electrode positioned on a longitudinal axis of the torch in electrical communication with the negative side of a power supply and having a longitudinally extending side surface and a bottom surface. The method generally comprises positioning opposed contact surfaces of the torch relative to each other generally within the primary gas flow path upstream from the bottom surface of the electrode to provide an electrically conductive path through the contact surfaces. The contact surfaces are then repositioned relative to each other to form a pilot arc therebetween in the primary gas flow path of the torch upstream from the bottom surface of the electrode. Working gas from a source of working gas is directed to flow through the primary gas flow path of the torch to blow the pilot arc downstream within the primary gas flow path toward the central exit orifice of the anode body.
Further, a shield cup of the present invention is adapted for use in a plasma torch of the type having a primary gas flow path for directing a working gas through the torch whereby the working gas is exhausted from the torch in the form of an ionized plasma and a secondary gas flow path for directing gas through the torch whereby the gas is exhausted from the torch other than in the form of an ionized plasma, with the torch having at least one metering orifice in the secondary gas flow path for metering the flow of gas through the secondary gas flow path. The shield cup is generally cup-shaped and is adapted for at least partially defining the secondary gas flow path. The shield cup is further adapted to define a tertiary gas flow path in fluid communication with the secondary gas flow path for further exhausting gas in the secondary gas flow path from the torch. The shield cup has at least one metering orifice in the tertiary gas flow path for metering the flow of gas through the tertiary gas flow path.
Other objects and features will be in part apparent and in part pointed out hereinafter.